Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing a first embodiment of our new design; and,

FIG. 2 is a front view of an alternate embodiment thereof.

The broken lines around the Figures show a display screen or portion thereof, and form no part of the claimed design. The broken lines within the Figures show portions of the graphical user interface that form no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 